PS 117 is 2 verses. 
- Theme is praise God
PS 118 is 29 verses
- Theme is Give thanks to the LORD
PS 119 is 176 verses (goes through the Hebrew alphabet)
- Theme is walking in the law of the LORD
from http://www.biblesummary.info/
Ps117: Praise the LORD! For great is his love towards us.
Ps118: Give thanks to the LORD; for his love endures forever! The nations surrounded me; I cut them off! The LORD has become my salvation.
Ps119: Blessed are those who walk in the law of the LORD. Teach me your decrees. I love your commands. Deliver me according to your promise.